Silencer



Aug. 18, 1959 Y D. E. HOLCROFT I 2,900,024

' SILENCER Filed Oct. 7, 1955 I 2 Sheets-Sheet 2 IN V EN TOR.

DONALD E. HOLCROFT Em BM,

United States Patent SILENCER Donald E. Holcroft, Chester, Pa., assignor to Scott Paper Company, Chester, Pa., a corporation of Pennsylvania Application October 7, 1955, Serial No. 539,181

16 Claims. (Cl. 162-371) trolling the noise generated by the subsequent rush of air into the perforations.

Another object of the present invention is to reduce the noise created on a paper-making machine.

' Another object is to provide a simple, inexpensive and effective silencer for a suction roll.

Still another object of the present invention is to provide a suction noise silencer which continues to provide effective silencing regardless of wear between the moving and the non-moving parts of the silencer.'

Further objects will be apparent by reference to the attached specifications, claims and drawings.

For the purpose of illustrating the invention, there are shown in the accompanying drawings forms thereof which are at present preferred, although it is to be understood that the various instrumentalities of which the invention consists can be variously arranged and organized and that the invention is not limited to the precise arrangements and organizations of the instrumentalities as herein shown and described.

In the drawings, where like reference characters indicate like parts: v

Figure 1 represents a fragmentary cross-sectional view of a portion of a suction roll and of a suction box and particularly of the packing glands, showing the silencer of the present invention.

Figure 2 represents a top plan view of one embodiment of the silencer of the present invention, supported on the upper end of the suction box side-wall shown in Figure 1.

Figure 3 is a, perspective view of one of the laminations of the preferred form of the silencer of the present invention shown in Figure 2.

Figure 4 is a fragmentary top plan view similar to that of Figure 5, showing another embodiment of the present invention.

Figure 5 is a view similar to Figure 4 showing still another modification of the present invention.

Figure 6 is a view similar to Figures 4 and 5, showing still another modification.

Figure 7 is a top plan view of another embodiment showing the manner in which the comb-like openings may be staggered.

Figure 8 is a view similar to-Figure 7 showing a skewed disposition of the teeth of the comb.

Figure 9 is a perspective view of the comb-like portion of the present invention, illustrating its manufacture from a single piece of material and also illustrating the manner in which the openings between the teeth taper to a point in two planes.

Figure 10 is a view similar to Figure 9 but showing curved-wall openings between the teeth of the comb.

For many years, manufacturers, engineers, production Patented Aug. 18, 1959 personnel and others using or having knowledge of present day manufacturing equipment have been aware of the problems caused by excessive noise (unwanted sound) attendant the effective and efficient operation of such equipment. In some industries this noise problem is more acute than others, as, for example, boiler factories, forges, jet engine testing, construction work, and the like. One field where the noise level is relatively high is the modern paper-making industry, where large, swiftly-moving, complex and noisy equipment is necessary to produce paper meeting present day quality specifications and production schedules. Over the past few decades, the technological advances in the paper industry have resulted in remarkab-le improvements in the speed and efficiency of the paper-making machines and one of the factors responsible for these improvements has been the development of suction press rolls and pressure rolls for removing moisture from the paper and the paper-carrying felts, for transferring the web of paper from one carrying felt to another carrying felt, and for removing water on the Fourdrinier wire by means of suction couch rolls. Suction rolls may also be used for other purposes not specifically cited above, such as felt cleaning and applicator rolls for special paper or felt treatment.

Such a suction roll is generally a heavy hollow cylinder which may have a resilient or corrosion resistant jacket overlying the outer surface and which is usually between 8 to 20' in length and from 20 to 48" in diameter with a multiplicity of radially extending holes passing through the shell or cylinder wall. In the rotatable cylinder an open-top box or suction chamber is supported in a manner which permits angular adjustment thereof with respect to a fixed reference point and which box is constructed and arranged whereby the free edges sealingly engage the inner surface of the shell. A partial vacuum is created within the box and the higher pressure (either higher air pressure or pressure created by a press roll or other pressure-inducing means) on the exterior of the shell forces water in the wrapping felts (overlying the cylinder at that place where the radially extending holes are in communication with the chamber) into the partially evacuated holes of the cylinder, in some cases, and in other cases merely helping to transfer'the web of paper from one carrying felt to the other carrying felt. The noise problem arises from the fact that some of the air in the radially extending holes in the area overlying the suction box is removed, and when the rotating shell carries these evacuated holes past the suction areas, the sudden rush of air at atmospheric pressure into the holes generates a high-pitched, unwanted sound. These unwanted sounds are usually 'of a high frequency, and although they are not the only unwanted sounds created by a paper-making machine, they contribute to hearing problems in the papermaking industry.

Although the technology of paper-making has advanced in recent years, relatively little attention has been paid to reducing the noises which cause hearing problems for the machine operators. Some of the earlier notable advances in the art are the contributions of Abbott & Krause at Ann Arbor, Michigan, and the work of the engineers at Beloit Iron Works, manufacturers of paper-making machinery. These prior developments sought, in some cases, to prevent the formation of the noise by controlling the rate at which the air at atmospheric pressure was returned to the evacuated holes in the rotating cylinders, and-in other cases, to suppress the noise by trapping it after it had once been created. However, the developments of the prior art had inherent limitations because the equipment was unwieldy and not usable under nor mal operating conditions, and because the equipment needed such fineadjustments and constant maintenance.

It is the purpose of the present invention to provide apparatus which prevents unwanted sounds from being generated, and which requires relatively little, if any, care and adjustment after installation.

In the present invention, a comb-like structure is mounted on the oifgoing edge of the vacuum box within a suction roll. This comb-dike member may be constructed in a variety of ways, but the general structure can be better understood by referring to the drawings, .wherein the numeral 22 indicates a suction roll cylinder having a relatively thick wall '23. The cylinder 22 has a plurality of holes 24 drilled in a generally radial direction through the wall 23; the holes 24 being communicating passages between the exterior surface of the cylinder 22 and the hollow interior thereof.

7 A suction box 26 is supported within the cylinder 22,

in a position adjacent the shell when the holes in the shell are covered by a felt 50 or by a press roll (not shown) or by any other means which providesresistance to the passage of air through the holes, and in a manner which permits limited angular movement of the box beneath said cover with respect to a fixed reference point. However, the cylinder 22 is independently mounted for free rotation with respect to the suction box.

The suction box 26 has two side-walls 27 and 28 extending generally axially within the cylinder 22, and each side-wall has an outer edge which terminates in a recess 29 and 32-, respectively, in spaced relationship to the inner surface 30 of the cylinder 22.

A generally conventional packing 31 is interposed in the recess 29 between the surface 30 and the edge of the wall 27 on the incoming side of the suction box and is resiliently urged, as by a spring 51, or any other suitable means against the surface 30 to provide a fluidtight seal between the side-wall 27 and the surface 30.

On the offgoing side 28 of the suction box 26 the recess 32 has dispose-d therewithin the comb-like silencer 33. The silencer 33 is formed of a plurality ofteeth or wedges 43, each having a generally radial portion 34 and a generally circumferential portion 35 which, preferably, is formed integrally with the radial portion to provide a generally L shaped member supported in the recess 32. The outer edge 36 of the portion 35 is curved in an are having substantially the same radius as the inner surface 30 of the cylinder 22 and this outer edge 36 is urged radially against the inner surface 30 by a resilient expansion member 37 which may be a spring or any other suitable means. Sealing rings 38 are interposed between the side-walls of the recess 32 and the side-walls of the portion 34 to provide a fluid-tight seal between the box side-wall 28 and the inner surface 30 of the cylinder. The silencer 33 extends along the full length of the suction box 26 and, in a preferred form, is composed of a plurality of wedges or laminations 43, assembled side by side and held together by a tie rod 39. The side-walls or faces 44 of the radially-extending portions 34 are generally parallel and permit stacking or assembly of the laminations. In the circumferentially-extending portion 35 of each lamination, the side-wallsor faces taper toward the offgoing edge 55, asat 56 and 57, so that each lamination 43 becomes increasingly thinner in the direction of the end 55 thereof. The side-Walls also taper in a vertical direction being thicker at he bottom than at the top, as is illustrated more clearly in Figures '2 and 3.

Of course, it is to be understood that the silencers 33 need not be formed of a plurality of laminations 43 as hereinabove described, but may be formed of a single block of material having the general cross-section shown in Figure 1, with a plurality of radially-extending V- shaped grooves 41 cut or otherwise formed in the circum-ferential portion 35.

Embodiments formed from SOllCl blocks are illustrtated in Figures 7', 8, 9 and 10.

Figures 4 to 10 inclusive show alternate shapes of the grooves 41. In Figlre 2 the grooves are generally V- shaped with non-curving side-walls and with the bisector of each groove lying in a plane extending at a right angle to the axis of the roll. In Figure 4 the bisector of each groove also lies in a plane extending at a right angle to the axis of the roll, but in this embodiment, the side-walls of each groove are generally curved.

In Figure 5 there is illustrated a modification of the groove formation shown in Figure 2; in this case the bisector of the side-walls is disposed at an angle to a plane extending at a right angle to the roll axis.

In Figure 6 one side-wall of the groove is straight and the other is curved, being a modification of the structure shown in Figure 5.

in Figure 7 the grooves are of varying length whereas in Figure 8 the grooves are of uniform length but skewed at an angle to the axis of the roll.

Figures 9 and 10 illustrate how the comb may be constructed so that the grooves fan out .in two or more planes from the apex, and, of course, it is to be understood that the relative shape or configuration of the grooves 41 is not to be limited to the embodiments shown, but that the unique feature of the structure of the present invention resides in placing the groove so that, although the curved surface 36 may be worn by reason of the rubbing of the inner surface 30 of the cylinder thereagainst, the effectiveness of the silencer is not impaired. This is because each of the side-walls of the many grooves 41 extends generally away from the inner surface of the cylinder as contrasted to the single groove shown in Abbott Patent 2,274,641 wherein the side-walls of the single gap extend parallel to the axis of the cylinder and wherein one side of the groove is formed by the inner surface of the cylinder itself.

The silencer of the present invention operates to prevent the formation of noise by creating a passageway of restricted dimensions through which the air moves from the area of atmospheric pressure into the partially evacuated holes 24 and is metered slowly into the holes 24 at a controlled rate so as to prevent the formation of unwanted sound. As the cylinder rotates, each hole 24, being at less than atmospheric pressure and being of a diameter greater than the minimum thickness of the lamination 43 at its surface 36, moves generally above the narrow root or apex of a groove in the silencer 33, and a very small quantity of air is metered into the evacuated holes through the groove. As the cylinder continues to rotate, the area of the metering opening increases as the hole passes along the groove, because at least one side-wall of each groove is disposed at an angle -to the direction of the movement of the hole passing over it, and the metering opening becomes increasingly larger to permit more and more: air at atmospheric pressure to be metered therethrough.

The metering characteristics of the grooves can be modified by changing the curvature of the side-walls, the angle of the grooves, or the length of the greoves, and thus the rate of flow of air into the holes can be predetermined or regulated.

Although the surface 36 may wear down, the function or operation of the silencer will not be impaired; it being desirable, however, to provide for periodic cleaning to remove the deposit of dirt, scum, rust, etc., which may be entrained in the air passing through the grooves of the comb. To this end, a cleaning port or conduit 42 may be provided in the silencer 33 with a portion of said conduit in communication with the roots of each groove 41 and through which conduit air under pressure or fluid under pressure may be forced so as to backwash the grooves and clean the foreign particles therefrom.

Furthermore, it is to be understood that the silencer 33 may be caster molded rather than being machined, and

also that it may be formed from anysuitable material whether metallic or nonmetallic, as, for example, a phenolic resin molded with a fibrous bonding material of a sort which provides a rigid, impact resistant and wear resistant material, susceptible of being lubricated with water. Micarta, nylon, Bakelite or Synthane are typical materials for this purpose.

Although the hereinabove discussions have been applied to suction roll and suction rolls especially of a single-wall solid shell, it is also to be understood that the invention herein has application with pressurized rolls as well as with suction rolls and may be described as having application for use in conjunction with any perforated sheet moving from a zone of one absolute pressure level to a zone of a second and different absolute pressure-level where pressure equalization takes place in the second zone. The moving sheet may be flat or curved, selectively, and hence may be a belt or plate instead of a cylinder.

Furthermore, the grooves 41 may be disposed in repeating pattern groups along the edge of the comb, as shown in Figure -7, may be skewed or placed along a line which is in a plane making an acute angle with the roll-axis, as shown in Figure 8, may be disposed in random pattern (not shown) or may be distributed in any pattern found to be desirable, which may be combinations of the patterns and teeth shown herein or may be any other pattern not shown but which follows the teaching of this invention. The disposition of the grooves is pre-determined so that in conjunction with the predetermined hole pattern on the moving cylinder or plate, the relationship between the holes in the cylinder or plate and the placement of the grooves is such that the generated sound is at a minimum.

In addition, though reference has been made herein to pressure-equalization on both sides of the moving perforated sheet, it is to be'understood that the sheet may be drilled with blind holes facing the suction box or with an over-wrap which acts as a valve to prevent complete equalization of pressure on both sides of the sheet and that the pressure equalization .therefore comprehends equalization between the pressure inside the holes and the pressure external to the sheet on the side to which the holes are exposed.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is therefore desired that the present embodiments be considered in all respects as illustrative and not restrictive, reference being had to the appended claims rather than to the foregoing description to indicate the scope of the invention.

Having thus described the invention, What is claimed 1. The combination of a perforate moving sheet, a suction box on one side of said sheet, and a silencer adjacent the suction box, said silencer being generally comb-like and having tapered teeth with the teeth lying in a plane generally parallel to the plane of the sheet and with the tips of the teeth pointing generally in the direction of movement of the sheet.

2. The combination of a perforate moving sheet, a suction box on one side of said sheet, and a silencer adjacent the off-going side of the suction box, said silencer being generally comb-like and having tapered teeth with the teeth lying in a plane generally parallel to the plane of the sheet and with the tips of the teeth pointing generally in the direction of movement of the sheet.

3. The combination of a perforate moving sheet, a. pressure-diiferential chamber on one side of said sheet,

the pressure in said chamber being difierent from the pressure around said chamber and on the opposite side of the sheet, and a silencer adjacent said chamber for controlling the equalizing of the pressure on both sides of said sheet, said silencer being generally comb-like and having tapered teeth with the teeth lying in a plane gen- 6 erally parallel to the plane of the sheet and with the tips of the teeth pointing generally in the direction of movement of the sheet.

4. The combination of a perforate moving sheet, a pressure-differential chamber on one side of said sheet, the pressure in said chamber being different from the pressure around said chamber and on the opposite side of the vsheet, and a silencer adjacent the off-going side of said chamber for controlling the equalizing of the pressure on both sides of said sheet, said silencer being generally comb-like and having tapered teeth with the teeth lying in a plane-generally parallel to'the plane of the sheet and with the tips of the teeth pointing generally in the direction of m ovem en-t of the sheet.

5. Asilencer for controlling the equalizing of pressure on opposite sides of a. perforate moving sheet, said silencer being generally comb-like and having tapered teeth with the teeth'lying in a plane, generally parallelto the plane of the sheet and with one side of said comb constructed and arranged for close sliding contact with said sheet and with the tips of the teeth pointing generally in the direction of movement of the sheet.

6. A suction roll silencer comprising a generally comblike body having a plurality of teeth formed thereon, one surface of said body being constructed and arranged for close contact with a perforate moving sheet, the teeth being tapered and the sides of adjacent teeth defining tapered gaps between adjacent teeth, said teeth lying in a plane generally parallel to'the plane of the perforate sheet, the narrow tips of the teeth pointing generally in the direction of movement of the sheet.

7. A suction roll silencer comprising a generally comblike body having a plurality of teeth formed thereon, one surface of said body being constructed and arranged for close contact with a perforate moving sheet, the teeth being tapered and the sides of adjacent teeth defining tapered gaps between adjacent teeth, said teeth lying in a plane generally parallel to the plane of the perforate sheet, the tips of the teeth pointing generally in the direction of movement of the sheet, at least one sidewall of each tooth being disposed at an angle to the direction of movement of said sheet.

8. A suction roll silencer comprising a generally comblike body having a plurality of'teeth formed thereon, one surface of said body being constructed and arranged for close contact with a perforate moving sheet, the teeth being tapered and the sides of adjacent teeth defining tapered gaps between adjacent teeth, said teeth lying in a. plane generally parallel to the plane of the perforate sheet, the tips of the teeth pointing generally in the direction of movement of the sheet, at least one sidewall of each tooth being convexly curved.

9. A suction roll silencer comprising a generally comblike body having a plurality of teeth formed thereon, one surface of said body being constructed and arranged for close contact with a perforate moving sheet, the teeth being tapered and the sides of adjacent teeth defining tapered gaps between adjacent teeth and with the tips of the teeth pointing generally in the direction of movement of the sheet, connecting portions between each of said teeth, each of said connecting portions spaced from said sheet and disposed in a plane which makes an angle with the plane of said sheet.

10. A suction roll silencer comprising a generally comblike body having a plurality of teeth formed thereon, one surface of said body being constructed and arranged for close contact with a perforate moving sheet, the teeth being tapered and the sides of adjacent teeth defining tapered gaps between adjacent teeth and with the tips of the teeth pointing generally in the direction of movement of the sheet, connecting portions between each of said teeth, each of said connecting portions being curved and forming one-half of the surface of a cone bisected by a plane passing through the axis of the cone.

11. A silencer constructed and arranged for use with a perforate moving sheet whereby to control the equalization of pressure on opposite sides of the sheet, said silencer consisting of a plurality of wedges disposed side by side to form a comlrlike structure with the wedges lying in a plane disposed generally parallel to the plane of said sheet and with the tips of the wedges pointing generally in the direction of movement of the sheet.

12. A suction roll silencer comprising a generally comb-like body having a plurality of teeth formed thereon, one surface of said body being constructed and ar- 'ranged for close contact with a perforate moving sheet, the teeth being tapered and the sides of adjacent teeth defining tapered gaps between adjacent teeth, said teeth lying in a plane generally parallel to the plane of the perforate sheet, the narrow tips of the teeth pointing generally in the direction of movement of the sheet, the wide ends of said teeth disposed in a line which is at an acute angle to the direction of movement of said sheet.

13. A suction roll silencer comprising a generally comb-like body having a plurality of teeth formed thereon, one surface of said body being constructed and arranged for close contact with a perforate moving sheet, the teeth being tapered and the sides of adjacent teeth defining tapered gaps between adjacent teeth, said teeth lying in a plane generally parallel to the plane of the perforate sheet, the narrow tips of the teeth pointing generally in the direction of movement of the sheet, the wide ends of said teeth having random disposition with respect to a straight line drawn at a right angle to the direction of movement of said sheet.

14. A suction roll silencer comprising a generally comb-like body having a plurality of teeth formed thereon, one surface of said body being constructed and arranged for close contact with a perforate moving sheet, the teeth being tapered and the sides of adjacent teeth defining tapered gaps between adjacent teeth, said teeth lying in a plane generally parallel to the plane of the perforate sheet, the narrow tips of the teeth pointing generally in the direction of movement of said sheet, the wide ends of said teeth being disposed in a line which is skewed with respect to a line drawn at a right angle to the direction of movement of said sheet.

15. The combination .of a perforate moving sheet, a pressure-difierential chamber ,on one side of said sheet, the pressure in the perforations and the chamber being substantially the same and being'difierent from the pressure external to the chamber, and a silencer adjacent said chamber for controlling the equalizing of the pressure external to the chamber and the pressure in the holes, said silencer being generally comb-like and having tapered teeth with the teeth lying in a plane parallel to the plane .of the sheet and with the tips of the teeth pointing generally in the direction of movement of the sheet.

16. A suction roll silencer comprising a generally comb-like body having a plurality of 'teeth formed thereon, one surface of said body being constructed and arranged for' close contact with a perforate moving sheet, the teeth being tapered and the sides of adjacent teeth defining tapered gaps between adjacent teeth, said teeth lying in a plane generally parallel to'the plane of the perforate sheet, the narrow tips of the teeth pointing generally in the direction of movement of the sheet, the

wide ends of some of said teeth disposed in a line which is at an actute angle to the direction of movement of said sheet and the wide ends of others of said teeth disposed in a line which is at a right angle to the direction of movement of said sheet.

References Cited in the file of this patent UNITED STATES PATENTS 

